Metal forming device and method



March 28, 1961 G. w. HARVEY ET AL 2,976,907

METAL FORMING DEVICE AND METHOD Filed Aug. 28, 1958 2 Sheets-Sheet 1 J M QMILKLKW March 28, 1961 w, HARVEY ETAL 2,976,907

METAL FORMING DEVICE AND METHOD 2 Sheets-Sheet 2 Filed Aug. 28, 1958 United States Patent METAL FORMING DEVICE AND METHOD George W. Harvey, La Jolla, and David F. Brower, Del Mar, Califi, assignors to General Dynamics Corporatron, New York, N.Y., a corporation of Delaware Filed Aug. 28, 1958, Ser. No. 757,867

11 Claims. 01. 153-40 The present invention relates generally to metal forming devices and methods and more particularly to a device in which metal may be formed by the energy acquired from a varying magnetic field and a method of forming with such energy.

A metal work piece can be formed into a desired shape by performing work on the metal, i.e.-,- by transferring sufiicient energy to' the metal so as tdshape the metal into the desired for'rn. Heretofore, metal work pieces have been shaped while cold either by applying a" relatively continuously increasing mechanical force to the metal being worked or by applying a series of mechanical impulses to the metal such as by swaging.

An object of the present invention is to provide a method and a device for forming metal in which the energy necessary for forming the metal work piece to a desired shape is acquired from a varying magnetic field. A further object of the present invention is to provide a metal forming device in which the metal work piece is formed in a desired manner by one or more force impulses set up by a varying magnetic field. Still another object of the present invention is to provide a metal forming device which is economical to manufacture, and rugged, durable and eflicient in operation.

Additional objects and advantages of the present invention will become apparent from the following description and appended claims.

. In the drawings:

Figural is a schematic perspective view of one embodiment of a metal forming device constructed in accordance with the present invention, this device being adapted to reduce the diameter of a tubular work piece;

Figure 2 is a reduced sectional view of the work piece shown in Figure 1 after the operation of the metal forming device of Figure l;

Figure 3 is a schematic perspective view of another embodiment of a metal forming device constructed in accordance with the present invention, this device being adapted to join together a pair of telescoping tubular members;

Figure 4 is a reduced sectional view of the interengaged tubular members shown in Figure 3 after the operation of the metal forming device of Figure 3;

Figure 5 is a schematic perspective view of another embodiment of a metal forming device which is adapted for forming a plurality of spaced circumferential crimps in a tubular work piece;

Figure 6 is a reduced sectional view of the work piece shown in Figure 5 after the operation of the metal forming device of Figure 5;

Figure 7 is a schematic perspective view, partially in section, of another metal forming device constructed in accordance with the present invention, which is adapted to form a design or pattern on a flat work piece;

Figure 8 is a reduced perspective view showing the surface of the work piece shown in Figure 7 after the operation of the metal forming device of Figure 7;

Figure 9 is a schematic perspective view, partially in section, of still another metal forming device constructed in accordance with the present invention, which is adapted for forming a tubular work piece into a specific hape in conformance with an outer mold; and

Figure 10 is a sectional view" of the tubular work piece shown in Figure 9 after operation of the metal forming device of Figure 9.

A metal forming device in accordance with the present invention includes a means for setting up a predetermined varying magnetic field, and a means for maintaining the metal to be formed within the magnetic field for a length of time such that suflicient energy is acquired by the metal to form the metal in the desired manner.

When a current carrying conductor is placed across a magnetic field, the conductor will be subjected to a pressure which will tend to move the conductor. The amount of pressure on the conductor is proportional to the product of the current through the conductor and the component of the magnetic field perpendicular to the current. This pressure acting" on the conductor over a certain distance is" equivalent to the energy density acquired by or the work performed per unit area on the conductor. If the current carrying conductor is held stationary in the magnetic field, the pressure acting on the conductor, if high enough, will cause the conductor to become deformed.

When a conductor is placed in a varying magnetic field, a current is induced in the conductor. The interaction between this current and the magnetic field will then subject the conductor to a force; If the conductor is constrained and if a sufiicient amount of energy is acquired by the conductor, the conductor will be deformed. The work performed on, or the energy acquired by the conductor depends upon the position of the con'- ductor relative to the magnetic field, the strength of the magnetic field, the current induced in the conductor, the mass of the conductor, internal forces within the conductor, and the frequency of variations in the magnetic field. Accordingly, a high instantaneous pressure may be applied to the conductor by utilizing a current pulse to set up the the magnetic field.

By shaping a conductor in a suitable form, and passing a current pulse therethrough', a magnetic field of a predetermined shape will be set up almost instantaneously (in the order of a microsecond). Metal positioned in the shaped magnetic field will be formed, if the necessary energy is transferred to metal, in a manner depending upon the shape of the magnetic field and the position of metal relative to the field. The duration of the pressure on the metal positioned in the magnetic field is dependent upon the duration of the pulse, and is limited by the allowable increase'in the temperature of the metal. Ordinarily, the pulse may be applied for a duration between approximately a microsecond and many microseconds. However, at very low ambient temperatures the pulse may be applied for a longer duration, ranging from microseconds to a minute or so. The desired form of the magnetic field will, of course, be determined by the shape of the work piece and the work which one wishes to'perform on the work piece. This Work may comprise shaping, welding, embossing, engraving, etc., and may be performed on the metal by means of a single magnetic impulse imparted to the metal or by means of a series of impulses, in the manner of swaging. Because of the instantaneous pressure on metal positioned in the magnetic field, the metal may be rapidly accelerated, and hence the metal may be moved at a high velocity. Such a magnetic field may be utilized in numerous applications (e.g., embossing a rapidly moving strip of material by instantaneously impelling the sheet against a die). The instantaneous pressure which can be applied by this method is very great and may be many times the elastic limit of the metal which is being formed, thereby causing the metal to flow after the termination of the impulse. I

The embodiments hereinafter described are particular n 3 applications of the principles of the invention to certain specific examples of metal forming.

The metal forming device shown in Figure 1 may be utilized in reducing the diameter of a portion of a tubular .work piece. In this device the varying magnetic field is set up by passing a current pulse through a coil or solenoid 11. While pulses can be provided in any desired manner, in the illustrated embodiment, one or more pulses are supplied by means of a pulsing network 12 which includes a high capacity condenser 13 in series with a switching means 14, such as an ignitron, thyratron, spark gap, etc. The condenser 13 may be charged by means of a suitable high-voltage supply 15 which is connected to the condenser through a switch means 16 and a current limiting resistor 17. A suitable cable, such as a coaxial cable 18, connects the pulsing network 12 to the solenoid 1.1.

A suitable tubular work piece 20 of a suitable conductive material, such as copper or aluminum, is fixedly positioned within the solenoid 11 by suitable means such as a pair of clamps 21 or the like. When a current pulse is applied to the solenoid 11 a varying magnetic field is set up which induces an electromotive force in the work piece 20 which, in turn, causes a high-current to flow around the work piece. If the energy transferred to the metal work piece 20 by the interaction of the induced current and the magnetic field is suflicient, the tubular wall of the portion of the work piece within the solenoid .11 will be forced inwardly into the general form shown in Figure 2. If desired, a suitable die (not shown) may be inserted into the work piece to define or limit the deformation of the work piece. Because of the high acceleration that can be developed in the work piece by this method, a die in the ordinary sense may not be necessary. In certain cases the die need not have great strength; instead, it may depend upon its mass alone to decelerate the work piece.

The amount of energy transferred to a certain work piece for a given solenoid can be increased by increasing the voltage applied to the condenser, increasing the capacity of the condenser, or increasing the number of pulses applied to the work piece.

In one embodiment of the above described metal working device the solenoid was constructed with turns of insulated copper wire having a cross sectional area of 1 square centimeter and had an internal diameter of 4 centimeters, an outer diameter of 6 centimeters, and a length of 12 centimeters. The source of current pulses was a 30 microfarad capacitor which was charged to 10 kilovolts. This device was used to deform copper tubing having an outer diameter of 3.5 centimeters and a wall thickness of approximately 1.5 millimeters.

A metal forming device which may be utilized for joining together a pair of telescoping tubes by suitably crimping the lapping portions of the tubes is illustrated in Figure 3. In this embodiment, a bar of conductive material is formed into a loop 22 and a current pulse is fed to the loop 22 through a coaxial cable 18a by means of a pulsing network 12a, similar to the one previously described in connection with the solenoid type metal forming device.

The interengaged portions of a pair of telescoping tubes 23 may be suitably positioned within the loop 22 by a pair of clamps 24 or the like. When a current pulse is passed through the loop 22 a concentrated magnetic field is set up which is capable of transferring sufiicient energy to crimp the tubes 23 as shown in Figure 4.

While in Figure 3 the loop type metal forming device is used to join a pair of telescoping tubes 23, it also can be used to join a tubular tube to a rod or be used in a swaging operation in which the loop and work piece are moved relative to each other, while passing a series of current pulses through the loop.

The efiect of the concentrated magnetic field set up by the loop type metal forming device on a tube is unique in that the length of the tube as a whole remains relatively constant and the wall thickness is increased as the diameter is decreased. This is accomplished without the necessity of utilizing a rigid and strong support. In mechanical swaging a similar efiect can only be obtained by utilizing heavy dies and forming equipment. Thus progressive swaging of a tube by the disclosed metal forming device results in an increased wall thickness with little change in length.

In one embodiment of the loop type metal forming device a A inch copper bar was formed into a loop with a /8 inch inside diameter. The pulsing network included two 30 microfarad capacitors connected in parallel which were charged to 10 kilovolts.

A plurality of spaced circumferentially extending crimps can be formed in a tubular work piece, as shown in Figure 6, by the embodiment of the metal forming device shown in Figure 5. In this arrangement a plurality of loops 25, similar to the loop 22 described above, are disposed sequentially along a'tubular work piece 26 of conductive material. These loops 25 are connected in parallel and the parallel arrangement is connected through a coaxial cable 18b to a source of current pulses such as a pulsing network 12b which may be similar to the pulsing network 12.

A further embodiment of a metal working device in accordance with the present invention is illustrated in Figure 7. This device is adapted for impressing a pattern into the surface of a flat sheet of conductive material. In this arrangement, a conductor is wound in the form of a flat spiral 27. The spiral 27 is connected through a coaxial cable 18c to a pulsing network 12c. A suitable die 28 is disposed in adjacent overlying relation to the spiral 27. Suitable means, such as a stand 29 having an adjustable upper head 30 and a raised platform 31, is provided to maintain the die 28 and the spiral 27 in a spaced-apart relationship.

A work piece 32, which is a relatively thin, flat sheet of conductive material, such as copper or aluminum, is arranged between the die 28 and the spiral 27. When a pulse is passed through the spiral 27 a varying magnetic field is set up, which induces an electromotive force in the work piece 32 causing local currents to flow therein. This sets up a force which forces the work piece 32 against the die 28, conforming it to the surface of the die, thus producing a pattern on the surface of the work piece. If desired, the metal working device may be operated in a vacuum to increase the efficiency of the forming of the metal. I

The spiral type metal working device may be used to strengthen metal by forming'ridges in the metal such as shown in Figure 8, to produce decorative designs in metal, to surface weld a metal sheet to a non-metallic sheet, etc.

In one embodiment of the spiral type metal forming device, a flat spiral was formed with approximately 14 turns of number 11 insulated copper wire. The spiral had an outer diameter of 5.5 centimeters. The current pulses for the spiral were provided by a 15 microfarad capacitor which was charged to 10 kilovolts. In one application of this spiral type metal forming device a .005 inch sheet of copper was conformed to a suitable pattern on the surface of a polyethylene die.

A still further embodiment of a metal forming device in accordance with the present invention is illustrated in Figure 9. This device is adapted for expanding a tubular work piece against a surrounding die. In this arrangement a conductor 33, which is generally semicylindrical in cross section with the edges rounded, is bent backwardly upon itself with the fiat pontions of the adjacent sections of the conductor facing each other. The conductor 33 is connected through a coaxial cable 18d to a pulsing network 12d. A suitable split tubular die 34, which is releasably locked together, is disposed in concentric relationship to the conductor 33.

A tubular work piece 35 is arranged between the conductor 33 and the die 34. When a current pulse is passed through the conductor 33 a generally circular circumferential field is set up along the length of the conductor. This sets up a force which expands the work piece 35 against the inner surface of the surrounding die 34, thus conforming the work piece to the pattern on the inner surface of the die, as shown in Figure 10.

In a practical embodiment of the metal forming device a generally semi-cylindrical conductor having a diameter of 2.5 centimeters, a gap of 2 millimeters between the flat surfaces, and a length of 15 centimeters, was utilized to set up the magnetic field. The source of current pulses was a 60 microfarad capacitor which was charged to kilovolts. The die had an internal diameter which just cleared the work piece having a diameter of 2.75 centimeters and a wall thickness of 0.5 millimeter.

From the above, it should be obvious that the principle of using a varying magnetic field to supply energy to form metallic objects can be applied to others forms of metal forming devices than those previously described.

Various of the novel features of the present invention are set forth in the following claims.

We claim:

1. A magnetic metal forming device comprising a conductor shaped to provide a predetermined magnetic field, means for applying at least one predetermined current pulse through said conductor, a die located adjacent said conductor, and means for positioning a metallic work piece between said conductor and said die, said current pulse being of such strength and being effective for a sufiicient length of time to transfer the necessary energy to the metallic work piece to cause it to conform to the surface of said die.

2. A magnetic metal forming device comprising a conductor wound in the shape of a fiat spiral, means for applying at least one predetermined current pulse through said conductor, a die located adjacent and generally parallel to the surface of said spiral, and means for maintaining the spaced relationship between said conductor and said die, said current pulse being of such strength and being effective for a sufiicient length of time to transfer the necessary energy to a sheet of metal positioned between said die and said conductor to cause it to conform to the surface of said die.

3. A magnetic metal forming device comprising a conductor bent back upon itself in hairpin fashion, means for applying at least one predetermined current pulse through the conductor, a tubular die surrounding at least a portion of said hairpin shaped conductor, said current pulse being of such strength and being effective for a sufiicient length of time-to transfer the necessary energy to a tubular metal work piece positioned over the conductor and within the die to cause it to conform to the surface of the die.

4. A method of forming metal comprising setting up a predetermined varying magnetic field, and maintaining a metal work piece within the magnetic field so that suflieient energy is transferred from the magnetic field to certain portions of the metal to form the metal in the desired manner.

5. A method of forming metal comprising applying a varying current through a conductor shaped to provide a predetermined magnetic field, and maintaining a metal work piece at a predetermined position within the magnetic field so that sufficient energy is transferred from the magnetic field to certain portions of the metal to form the metal in the desired manner.

6. A method of forming metal comprising applying at least one current pulse of a predetermined amplitude and duration through a conductor shaped to provide a magnetic field of a predetermined shape, and maintaining a metal work piece at a predetermined position relative to the conductor so that the changing magnetic field will act in the desired manner on the work piece, the magnetic field at the work piece being of such strength and shape and being effective for a length of time sufficient to transfer the necessary energy to certain portions of the metal to form the metal in the desired manner.

7. A magnetic metal forming device comprising a conductor shaped to provide a magnetic field of a predetermined shape, an energy storage means, switch means conneoting said conductor to said energy storage means, and means for maintaining a metal work piece to be formed at a predetermined position within the magnetic field produced by said conductor when said switch means is closed, the energy in said energy storage means being such that the produced magnetic field is of sufiicient amplitude and effective for a length of time sufficient to transfer the necessary energy to certain portions of the metal work piece to form the metal work piece in the desired manner.

8. A magnetic metal forming device comprising a conductor shaped to provide a magnetic field of a predetermined shape, a capacitor, switch means connecting said conductor to said capacitor, means connected to said capacitor for storing electrical energy in said capacitor, and means for maintaining the metal work piece to be formed at a predetermined position in the magnetic field produced by said conductor when said switch means is closed, the energy stored in said capacitor being such that the produced magnetic field is of sufficient amplitude and effective for a length of time sufficient to transfer the necessary energy to certain portions of the metal work piece to form the metal work piece in the desired manner.

9. A magnetic metal forming device comprising a solenoid, energy storage means, switch means connecting said solenoid to said energy storage means, and means for positioning at least a part of an elongated metallic work piece within said solenoid, the energy in said energy storage means being such that the magnetic field produced by said solenoid when said switch means is closed is of sufficient amplitude and effective for a length of time sufficient to transfer the necessary energy to the metal work piece within the solenoid to alter its cross sectional area.

10. A magnetic metal forming device comprising at least one conductor shaped so as to form at least one loop, an energy storage means, switch means connecting said loop to said energy storage means, and means for positioning at least a portion of a metallic work piece to be formed within said loop-shaped conductor, the energy in said energy storage means being such that the magnetic field produced by said loop-shaped conductor when said switch means is closed is of suificient amplitude and effective for a length of time sufficient to transfer the necessary kinetic energy to the metal work piece within said loop-shaped conductor to alter its cross sectional area.

11. A magnetic metal forming device comprising a low resistance, rigid solenoid, a high voltage source capable of passing a high current through said solenoid, switch means connecting said solenoid to said high voltage source, and means for fixedly positioning at least a part of an elongated tubular metallic work piece within said solenoid, said source of high voltage being such that the current through said solenoid when said switch means is closed produces a magnetic field which is of suflicient amplitude and elfective for a length of time suflicient to transfer the necessary energy to the metal work piece within the solenoid to alter its cross sectional area.

References Cited in the file of this patent UNITED STATES PATENTS 1,365,198 Sessions Ian. 11, 1921 2,367,206 Davis Jan. 16, 1945 2,372,516 Rechton Mar. 27, 1945 2,397,717 Westin Apr. 2, 1946 2,441,517 Sussman May 11, 1948 2,686,865 Kelly Aug. 17, 1954 

